The present invention relates to a method and device for discriminating different types of ground vegetation in agriculture and relates particularly, but not exclusively, to an agricultural spraying apparatus which incorporates such a device. Whilst the invention will be described with particular reference to an agricultural spraying apparatus for spraying herbicides, it will be appreciated that the same method and device for discriminating different types of ground vegetation may be employed in other applications, for example, for applying fertilisers, or other pesticides, and for conducting surveys of ground vegetation.
In its application to the spraying of agricultural herbicides the device can provide the following advantages over known techniques for discriminating ground vegetation. The process of distinguishing different types of ground vegetation or coverage can be effected independently of ambient light conditions, ie, varying sunlight conditions will not affect the readings. Signal processing is very rapid as only a single comparison of values is made, thus facilitating rapid decision making on-the-fly. No monitoring of ground speed is required as each spray nozzle is activated for the duration of sensing the presence of a weed in the target area only. The volume per acre of herbicide required can be vastly reduced as the application of herbicide is precisely targeted to weeds only. Refilling of the tank on the boom spray is thus also minimised.
Over the last couple of decades broadacre spraying has become an essential component of crop management on most farms in Australia. Chemical companies have developed new chemical pesticides for killing weeds, insect pests and diseases which attack cash crops. The most commonly used technique for broadacre spraying of pesticides is the use of boom sprays, which may be self-propelled or towed behind another vehicle. A typical boom spray has a plurality of spray nozzles mounted at spaced locations along a boom, a. large tank for containing the spray liquid and a pump system for pumping the liquid to the nozzles. A control system is often provided for controlling the rate at which the pesticide is sprayed relative to ground speed, and a marker system may be used to aid driving and avoid overlapping.
One of the disadvantages of conventional boom sprays is that herbicides are sprayed indiscriminately on both the crop, bare ground and weeds. This is of concern in the case of food crops, with consumer groups becoming increasingly vocal about chemical residue in crops and livestock. There is also an economic disincentive since a much greater volume of chemical spray must be applied per acre than is actually required to effectively control the weeds.
Various attempts have been made to allow for more discriminate spraying of herbicides. U.S. Pat. No. 5,144,767 discloses a controller for agricultural sprays developed by The Division of Plant Industries, New South Wales Agriculture and Fisheries. U.S. Pat. No. 5,144,767 discloses an agricultural spray which is controlled by an apparatus having a sensor for determining the irradiance in the red and near infra-red bands of the electromagnetic spectrum, and a plurality of sensors for determining the radiance of a target area in the red and near infra-red wave bands. A controller controls the individual sprays by comparing the ratios of the radiance to the irradiance (reflectance) in each band respectively, and determining if the spray for a particular target area should be turned on or off. The determination may be made by referring to a stored look-up table of reflectance values, or by carrying out the calculations of non-linear decision algorithms. Reflectance is defined as the ratio of reflected energy to incident energy.
In U.S. Pat. No. 5,144,767 reflectance is adopted as the decision-making criteria, rather than radiance, in order to overcome problems in the variability of radiance measurements caused by changing ambient light conditions. In direct sunlight a significant component of the irradiance (incident sunlight) on the earth""s surface is in the red and near infra-red wave bands. However, in cloudy conditions there is a significant decrease in the amount of infra-red radiation reaching the Earth""s surface due to absorption by atmospheric moisture and clouds. It is thought that reflectance should stay approximately the same under varying light conditions for a particular target. Nevertheless, in practice there can still be considerable variability in the calculated reflectance value as the amount of sunlight irradiating the target area will vary relative to the amount of sunlight irradiating the irradiance sensor. This occurs because the target area is located underneath the apparatus and will therefore intermittently be in shadow and in direct sunlight, depending on the direction of travel of the boom spray.
The present invention was developed with a view to providing an improved device and method for discriminating different types of ground vegetation that is more reliable than prior art techniques.
According to one aspect of the present invention there is provided a device for discriminating different types of ground vegetation, the device comprising:
an artificial source of electromagnetic radiation for directing a beam of radiation onto the vegetation;
a plurality of sensors for detecting radiation from said radiation source reflected onto each of said sensors from the vegetation in a selected frequency band and generating a sensing signal from each sensor in response to said detection, and wherein said plurality of sensors are arranged in a sensor array with a geometric configuration adapted to aid in discriminating different types of vegetation; and,
signal processing means for determining whether a magnitude of each said sensing signal falls within a predetermined range of values whereby, in use, one type of vegetation can be distinguished from another type based on the magnitudes of said sensing signals.
Preferably the device further comprises a shroud for minimising the amount of sunlight reflected from the vegetation.
In a preferred embodiment said selected frequency band is in the infra-red portion of the electromagnetic spectrum, and said predetermined range of values is set to enable a type of weed plant to be distinguished from a crop plant. Preferably said selected frequency band is in the infra-red portion of the spectrum having a wavelength within the range of 450 nm to 10 xcexcm. The most preferred frequency band is in the near infra-red waveband of approximately 650 nm to 2000 nm.
Preferably said artificial radiation source produces a beam of substantially collimated light. Typically said sensor is a photodiode adapted to provide a sensing signal in response to detected radiation in the near infra-red wave band. Preferably sensors capable of providing a sensing signal in response to detected radiation in the visible and/or ultra-violet (UV) wave bands are also employed.
Preferably said signal processing means determines whether a magnitude of the sensing signal falls within a predetermined range of values (a sensing window) which is specific to each sensor in the sensor array. Preferably each sensor in the sensor array has a sensing window that is unique to that sensor.
According to another aspect of the present invention there is provided a method for discriminating different types of ground vegetation, the method comprising:
directing a beam of electromagnetic radiation from an artificial source onto the vegetation;
providing a plurality of sensors arranged in a sensor array with a geometric configuration adapted to aid in discriminating different types of vegetation;
detecting radiation from said artificial source reflected from the vegetation onto each of said sensors in a selected frequency band and generating a sensing signal from each sensor in response to said detection; and,
determining whether a magnitude of each said sensing signal falls within a predetermined range of values whereby, in use, one type of vegetation can be distinguished from another type based on the magnitude of said sensing signals.
Preferably the method further comprises the step of:
shading the vegetation from direct sunlight so as to minimise the amount of sunlight reflected from the vegetation.
According to a still further aspect of the present invention there is provided an agricultural spraying apparatus for spraying ground vegetation, the apparatus comprising:
a spraying means for delivering a liquid spray to ground vegetation;
an artificial source of electromagnetic radiation for directing a beam of radiation onto the vegetation;
a plurality of sensors for detecting radiation from said radiation source reflected onto each of said sensors from the vegetation in a selected frequency band and generating a sensing signal from each sensor in response to said detection, and wherein said plurality of sensors are arranged in a sensor array with a geometric configuration adapted to aid in discriminating different types of vegetation; and,
signal processing means operatively connected to said sensor array and spraying means for determining whether a magnitude of each said sensing signal falls within a predetermined range of values, and for actuating said spraying means when a particular type of vegetation is distinguished from another type based on the magnitudes of said sensing signals.
Preferably the apparatus further comprises a shroud for shading the vegetation and minimising the amount of sunlight reflected from the vegetation.
Typically said spraying means includes a plurality of spray nozzles and a corresponding plurality of electro-magnetically actuated valves for controlling the delivery of said liquid spray through each nozzle. Advantageously said radiation source and sensor are one set of a plurality of sets of radiation sources and sensors, a respective set being provided adjacent each of said spray nozzles.